<HTML><HEAD><TITLE>^(+Number1, +Number2, -Result)</TITLE>
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<H1>^(+Number1, +Number2, -Result)</H1>
Evaluates the expression Number1 "to the power of" Number2 and unifies the
resulting value with Result.


<DL>
<DT><EM>Number1</EM></DT>
<DD>A number.
</DD>
<DT><EM>Number2</EM></DT>
<DD>A number.
</DD>
<DT><EM>Result</EM></DT>
<DD>A variable or a number.
</DD>
</DL>
<H2>Description</H2>
   This predicate is used by the ECLiPSe compiler to expand evaluable
   arithmetic expressions.  So the call to ^(Number1, Number2, Result) is
   equivalent to
<PRE>
    Result is Number1 ^ Number2
</PRE>
    which should be preferred for portability.
<P>
   The result is of type float if any of the arguments is a float. 
   When an integer is raised to the power of a negative integer, the
   result type depends on the value of the global flag prefer_rationals.
   If it is on, it is a rational, otherwise a float.  When the exponent
   is not an integer, the result is of type float.

<P>
   In coroutining mode, if Number1 or Number2 are uninstantiated, the call
   to ^/3 is delayed until these variables are instantiated.

<P>

<H3>Modes and Determinism</H3><UL>
<LI>^(+, +, -) is det
</UL>
<H3>Exceptions</H3>
<DL>
<DT><EM>(4) instantiation fault </EM>
<DD>Number1 or Number2 is not instantiated (non-coroutining mode    only).
<DT><EM>(24) number expected </EM>
<DD>Number1 or Number2 is not of a numeric type.
<DT><EM>(20) arithmetic exception </EM>
<DD>Illegal arithmetic operation:  Number1 is negative and    Number2 is no integral number.
<DT><EM>(20) arithmetic exception </EM>
<DD>Illegal arithmetic operation:  Number1 and Number2 are both    zero.
</DL>
<H2>Examples</H2>
<PRE>
Success:
      ^(5, 3, 125).
      ^(-5, 3, -125).
      ^(5, -2, 0.04).
      ^(5, 2.2, 34.493244).
      ^(5.0, 2, 25.0).
Fail:
      ^(1, 2, 3).
      ^(1, 2, 3.0).
      ^(5, 2, r).
Error:
      ^(A, 2, 6).             (Error 4).
      ^(-5, 0.5, X).          (Error 20).
      ^(2 + 3, 2, 25).        (Error 24).



</PRE>
<H2>See Also</H2>
<A HREF="../../kernel/arithmetic/is-2.html">is / 2</A>, <A HREF="../../kernel/env/get_flag-2.html">get_flag / 2</A>, <A HREF="../../kernel/env/set_flag-2.html">set_flag / 2</A>
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